Suss out is a slang verbal phrase meaning to figure out, discover, understand something or to get to know someone’s true nature.
“Suss out” was the commonly used expression among beatniks in the 1960s according to the Dictionary of Contemporary Slang and derives from ‘suspect’ according to both Merriam-Webster’s Collegiate Dictionary (11th ed.) and The American Heritage Dictionary of the English Language (4th ed.)
Despite the early origin, the expression has started to become commonly used since 2000 according to Ngram, and got popular thanks to the online videogame Among Us released in 2018. Though, Among Us used the word ‘sus’ as the abbreviation of ‘suspicious’. The adjective was a trending expression in gamechats, on Twitter and Reddit, the verb phrase “ suss out” has reached its top popularity as well, with the meaning ‘identifying suspicious acting’ according to Urban Dictionary.
The verb phrase can still be frequently seen on Twitter, Reddit, Instagram, and Facebook.
“Toronto women turn to ‘Unhinged’ dating list to suss out problematic men” posted by u/LZBUM in subreddit r/Toronto.